The present invention and its underlying object are explained based on micromechanical microphone/pressure sensor systems, although they are in principle applicable to any arbitrary micromechanical sensor system combinations.
Micromechanical microphone systems usually have a sound transducer which is integrated on an MEMS chip for converting sound energy into electrical energy, in which a first electrode which is deflectable by sound energy and a stationary, perforated second electrode are capacitively interacting. The deflection of the first electrode is determined by the difference between the sound pressures upstream and downstream from the first electrode. If the deflection changes, the capacitance of the capacitor formed by the first and the second electrodes is changed, which is metrologically detectable.
On the back side of the first electrode, a so-called back volume is provided. The size of the back volume determines the sensitivity of the micromechanical microphone system, since a compression in the back volume, in particular in the case of small back volumes, which is caused by the deflection of the first electrode has a damping effect on the deflection of the first electrode.
Micromechanical microphone systems, such as the ones used in mobile devices, in smart phones, for example, are generally available in two design variants, such as from US 2013/0147040 A1, for example.
In the case of the “bottom port” variant, the acoustic access is implemented from the bottom via a printed circuit board. In this case, the MEMS chip including the sound transducer is glued to the printed circuit board and closed using a back cover in order to form the back volume.
In the case of the “top port” variant, the acoustic access takes place from the top; the MEMS chip including the sound transducer is glued into a cover, so that the acoustic access takes place through a port in the cover.
The overall size is playing an increasingly important role for more recent applications, e.g., headsets or electronic eyeglasses. It is important in this case to achieve what may be a large back volume with a minimal base area and overall height, since the back volume significantly contributes to the overall performance of the microphone.
Due to the manufacturing tolerances in the case of the known approaches for the housing, a further miniaturization while maintaining the overall performance is not possible for the time being. In addition, the maximally possible back volume and the maximum size of the access port are not achieved either due to the tolerances.
It is known from DE 10 2006 022 379 A1 to bond an ASIC chip including a back-side cavern on an MEMS chip including a sound transducer in such a way that the back volume is increased by the cavern because it is distributed among both chips.
A wafer level-based packaging concept for MEMS components is from DE 10 2011 005 676 A1, an interposer which has at least one passage opening as the access opening to the MEMS component, e.g., a sound passage opening, being connected to the front side of the MEMS component. The interposer is provided with electrical vias, so that the MEMS component is electrically connectable via the interposer.